This invention relates to a technique of polymerizing calixarene tetramer (as referred to calix [4] arene), and a technique of selectively separating divalent lead ions from an aqueous solution containing a variety of ions by forming an inclusion compound composed of the calix [4] arene polymer and the lead ions included therein.
A technique of separating lead ions from ions other then the lead ions is very important in order to remove harmful metals from environment and to remove impure metals in manufacturing a highly pure metal used for electric and electronic materials.
Meanwhile, calixarene compounds have been noted as the third big cyclic inclusion compound next to cyclodextrin and crown ether on account of their faculties for recognition and separation of molecules or ions since Gutsche et. al. in U.S. developed a method of synthesizing them at a low cost in 1978.
However, because the compounds have a low solubility in an organic solvent, it is not suitable to use them as an extracting medium for solvent extraction.
Therefore, it is practical to use the compounds as an adsorbent or separating membrane in the solid state in order to selectively recognizing and separating a trace amount of specific substances.
Thus, there is a technique of separating optical isomers in a chromatography in which adsorbents are made up of a variety of calixarene compounds fixed on water-insoluble supports such as glycidyl methacrylate (see: Showa Denko K. K., JP-A-6-58920 and JP-A-5-264531).
However, since in the above technique a rate of a functional group in the calixarene is only 20 mmol per kg of dried adsorbent, it is too low to use it as the adsorbent of metal ions.
Meanwhile, the inventors have developed a method of fixing calixarene carboxylic acid derivatives on polyallylamine and a method of adsorbing and separating divalent lead ions using the same (see: JP-A-11-70383).
However, the developed adsorbent may adsorb metal ions other then divalent lead ions depending on treatment conditions because of the presence of remaining primary and secondary amines in the adsorbent. Further, since its exchange capacity for lead ions is only several hundreds mmol per kg of the dried adsorbent, it is desired to increase the capacity.
An object of the invention is, therefore, to develop an adsorbent having a excellent selectivity for divalent lead ions, an easy preparation, and a low cost and whereby to provide a technique of more efficiently separating, removing and recovering the lead ions from an aqueous solution containing the lead ions.
As a result of the inventors"" hard study for the purpose of attaining the above object, the inventors have found a new method of polymerizing or resinifing calixarene and further have found that the polymerized or resinified compound has a high selectivity for the divalent lead ions, and accomplished the invention.
Thus, the present invention has the following construction.
(1) A calix [4] arene polymer according to the present invention has a repeating unit shown by the following chemical formula. 
An unbonding hand in the formula combines with other calix [4] arene being the repeating unit and benzene rings thereof combine with each other through a methylene group to construct a network. Besides, the number of the repeating unit is preferably 10-1000.
(2) An adsorbent according to the present invention is characterized by being composed of the aforementioned calix [4] arene polymer.
(3) An inclusion compound according to the present invention is characterized by composed of the aforementioned calix [4] arene polymer and divalent lead ions included therein.
(4) A method of manufacturing the aforementioned calix [4] arene polymer according to the present invention is characterized by comprising the steps of mixing calix [4] arene shown by the following chemical formula, trioxane and acetic acid to stir them under heating, adding a mixture of sulfuric acid and acetic acid thereto to further stir them under heating, and after cooling it, precipitating a product by adding sodium hydrogencarbonate thereinto 
(5) A method of separating divalent lead ion according to the present invention is characterized by using the aforementioned calix [4] arene polymer as an adsorbent for divalent lead ions.
In a practical adsorbing procedure, a batch process can be conducted in which a predetermined amount of an adsorption gel made up of the polymer according to the present invention is placed into a tank together with an aqueous solution to be treated, to adsorb divalent lead ions under stirring, and then the gel is separated by filtrating. Alternatively, a continuous process can be conducted in which an adsorbent made up of the polymer according to the present invention is packed into a column and an aqueous solution to be treated is passed through the column to adsorb divalent lead ions.
After the lead ions are removed, the aqueous solution can be released to environment, or further can be treated to recover useful metal ions, if contained.
On the other hand, the lead can be recovered at a high purity and concentration by contacting the adsorbent adsorbing the lead with, for example, an aqueous solution of concentrated nitric acid.